lib/test_linear_ranges: add a test for the 'linear_ranges'

    Add a KUnit test for the linear_ranges helper.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Link: https://lore.kernel.org/r/311fea741bafdcd33804d3187c1642e24275e3e5.1588944082.git.matti.vaittinen@fi.rohmeurope.com


Signed-off-by: Mark Brown <broonie@kernel.org>